Decimal place value

Here you will learn about decimal place value, including the names and values of the different positions.

Students will first learn about decimal place value as part of their work with numbers and operations in base ten in elementary school.

What is decimal place value?

Decimal place value extends our understanding of place value to the decimal system, which are the digits to the right of the decimal point.

To do this, look at the connection between fractions and decimals.

For example,

This model shows \cfrac{4}{10}.

We can also write this as the decimal 0.4. We read it as “four-tenths,” just like the fraction.

That is because the first decimal place is tenths.

Let’s look at the next decimal place.

For example,

This model shows \cfrac{4}{100}.

We can also write this as the decimal 0.04. We read it as “four-hundredths,” just like the fraction.

That is because the second decimal place is hundredths.

Let’s look at the next decimal place.

For example,

This model shows \cfrac{4}{1,000}.

We can also write this as the decimal 0.004. We read it as “four-thousandths,” just like the fraction.

That is because the third decimal place is thousandths.

Here are the first three decimal place values. They show us the value of each digit in the number.

Notice the pattern in the denominators:

to to

As the places become smaller, each is \cfrac{1}{10} the size of the place to its left.

As the places become larger, each is 10 times the size of the place to its right.

These are the same patterns you see with whole numbers.

What is decimal place value?

Common Core State Standards

How does this relate to 4th grade math and 5th grade math?

• Grade 4 – Numbers and Operations – Fractions (4.NF.C.6)
  Use decimal notation for fractions with denominators 10 or 100. For example, rewrite 0.62 as \cfrac{62}{100} ; describe a length as 0.62 meters; locate 0.62 on a number line diagram.

• Grade 5 – Numbers and Operations in Base 10 (5.NBT.A.1)
  Recognize that in a multi-digit number, a digit in one place represents 10 times as much as it represents in the place to its right and \cfrac{1}{10} of what it represents in the place to its left.

How to use decimal place value

In order to write a fraction as a decimal:

1. Write the fraction in words.
2. Place the numerator of the fraction on the place value chart.
3. Write the decimal number.

In order to write a fraction as a decimal:

1. Write the decimal in words using a place value chart.
2. The digits of the decimal will be the numerator, and the denominator is where the last digit of the decimal is in the place value chart.
3. Write the fraction.

In order to write the value of a digit in a decimal number:

1. Locate the digit within the number.
2. Use the place value chart to find the position.
3. Write the value of the digit.

In order to compare the value of a digit in two decimal numbers:

1. Locate the digits within the number(s).
2. Use the place value chart to find the positions.
3. Compare how many times bigger or smaller the positions are.

Decimal place value examples

Example 1: write a fraction as a decimal

Write \cfrac{2}{10} as a decimal.

1. Write the fraction in words.

\cfrac{2}{10} is 2 tenths.

2Place the numerator of the fraction on the place value chart.

Put a 2 in the tenths place.

3Write the decimal number.

\cfrac{2}{10} written as a decimal is 0.2

Example 2: write a fraction as a decimal

Write \cfrac{51}{100} as a decimal.

Place the numerator of the fraction on the place value chart.

The model shows \cfrac{51}{100}.

In the model there are 5 full columns of 10, which is equal to 5 tenths.

So to write this decimal, put a 5 in the tenths place and 1 in the hundredths place.

Example 3: writing a decimal as a fraction

Write 0.22 as a fraction.

Write the decimal in words using a place value chart.

0.22 is 22 hundredths.

The digits of the decimal will be the numerator, and the denominator is where the last digit of the decimal is in the place value chart.

The model shows 22 hundredths.

The 22 in the decimal is the numerator.

The last place value position is hundredths (which is also the size of the 22 parts), so this is the denominator.

Example 4: write the value of a decimal digit

What is the value of the digit 3 in 0.13?

Locate the digit within the number.

Use the place value chart to find the position.

Example 5: write the value of a decimal digit

What is the value of the digit 7 in 0.75?

Locate the digit within the number.

Use the place value chart to find the position.

Example 6: compare the value of the same digit in a different place

Compare the value of each digit 1 in the number 0.101.

Locate the digits within the number(s).

Use the place value chart to find the positions.

Compare how many times bigger or smaller the positions are.

In 0.101, there is a digit 1 in the tenths position and in the thousandths position.

0.1 is 100 times greater than 0.001.

0.001 is 100 times smaller than 0.1. The 1 in the thousandths is \cfrac{1}{100} the value of the 1 in the tenths.

Teaching tips for decimal place value

• Instead of relying on just worksheets, use manipulatives to help students visualize the size of each place value and see how each position relates to the others. For smaller positions, especially thousandths, digital representations may be the best option.

• Decimal place values in our number system are based on patterns, which many students will discover as they work. Ask questions such as “What do you notice about these numbers?” or “If you change the place value of the digits, how does the value of the number change?” to guide all students to see the underlying structure of our place value system.

• Incorporate decimal place value ideas daily. It can be something as simple as a quick place value game. For example, say to students “I am thinking of a number that has more than 7 tenths, what could it be?” Daily activities like this help students to think flexibly about decimal place value.

• Ask students to show the standard form, expanded form, and word form for any given decimal to reinforce the connection between each representation.

• Have a decimal place value chart posted in the classroom or another way that is easily accessible to students. Seeing a chart regularly can help students remember it.

Our favorite mistakes

• Writing more than one digit in a place
  Just like with whole number place value, decimal place only has one digit per place.
  For example,
  Writing \cfrac{51}{100} as 0.051 is read as 51 thousandths, not 51 hundredths. The digits 5 and 1 cannot both go into the hundredths place. You place 5 in the tenths place, because \cfrac{50}{100}=\cfrac{5}{10}.

• Thinking there is a “oneths” place
  The first place value position to the right of the decimal point is the tenths column, not the “oneths” column.
  For example, In the number 1.534, what is the value of the digit 3?
  Three tenths or 0.03 \color{red} ✘ Three hundredths, or 0.03 \color{green} ✔
  (Treating the first decimal (Treating first decimal place as tenths
  place as “oneths” and the and the second as hundredths)
  second as tenths)

• Confusing the hundredths and hundreds places
  The numbers to the right of the decimal point end in ‘ths’ because they are parts of a whole. The numbers to the left of the decimal point do not end in ‘ths’ because they are whole.
  
  

  

Related lessons on decimals

• Decimals
• Decimal number line
• Decimal places
• Adding decimals
• Multiplying and dividing decimals
• Multiplying decimals
• Dividing decimals
• Adding and subtracting decimals
• Subtracting decimals
• Comparing decimals

The next lessons are

• Exponents
• Algebraic expression
• Math equations
• Rounding decimals
• Percent
• Converting fractions, decimals, and percentages

Still stuck?

At Third Space Learning, we specialize in helping teachers and school leaders to provide personalized math support for more of their students through high-quality, online one-on-one math tutoring delivered by subject experts.

Each week, our tutors support thousands of students who are at risk of not meeting their grade-level expectations, and help accelerate their progress and boost their confidence.

Find out how we can help your students achieve success with our math tutoring programs.